1. Field of the Invention
The present invention relates to a device and a method for controlling ignition timing of an internal combustion engine, and particularly relates to a technique of determining whether knocking is present or absent based on a waveform of vibration and magnitude of vibration of the internal combustion engine and retarding ignition timing in accordance with a determination result.
2. Description of the Background Art
Conventionally, various methods of detecting knocking (knock) generated in an internal combustion engine have been proposed. For example, there is a technique of determining occurrence of knocking if magnitude of vibration of an internal combustion engine is greater than a threshold value. However, even if knocking has not occurred, there may be a case where magnitude of noise such as vibration generated when an intake valve or an exhaust valve is closed, for example, is greater than the threshold value. In this case, it may erroneously be determined that knocking has occurred even though knocking has not occurred. Accordingly, there has been proposed a technique of determining whether knocking is present or absent based on a waveform of vibration so as to consider properties other than the magnitude, such as a crank angle at which vibration is generated and a damping rate.
Japanese Patent Laying-Open No. 2005-330954 discloses a device for determining knocking of an internal combustion engine, which device precisely determines whether or not knocking has occurred by using a waveform of vibration. The device for determining knocking described in Japanese Patent Laying-Open No. 2005-330954 includes a crank angle detection unit for detecting a crank angle of an internal combustion engine, a vibration detection unit for detecting a value related to magnitude of vibration of the internal combustion engine, a waveform detection unit for detecting a waveform of the vibration of the internal combustion engine between predetermined crank angles, based on the value related to the magnitude of the vibration, a storage unit for storing in advance a waveform of vibration of the internal combustion engine, and a determination unit for determining whether or not knocking has occurred in the internal combustion engine based on a result of comparison between the detected waveform and the stored waveform. The determination unit determines whether or not knocking has occurred based on whether or not knock magnitude, which is a product of a value representing a deviation of the detected waveform and the stored waveform from each other and a value representing the magnitude of the vibration, is greater than a determination value.
According to the device for determining knocking described in this publication, the crank angle detection unit detects a crank angle of the internal combustion engine, the vibration detection unit detects a value related to magnitude of vibration, and the waveform detection unit detects a waveform of the vibration of the internal combustion engine between predetermined crank angles, based on the value related to the magnitude of the vibration. The storage unit stores in advance a waveform of vibration of the internal combustion engine, and the determination unit determines whether or not knocking has occurred in the internal combustion engine based on a result of comparison between the detected waveform and the stored waveform. Accordingly, it is possible to form and store in advance a knock waveform model, which is a waveform of vibration when knocking is generated by experiment, for example, and compare this knock waveform model and the detected waveform to thereby determine whether or not knocking has occurred. Therefore, it becomes possible to analyze in more detail whether or not the vibration of the engine is caused by knocking. Furthermore, it is determined whether or not knocking has occurred based on magnitude of the vibration as well as the waveform of the vibration. Consequently, it becomes possible to precisely determine whether or not knocking has occurred.
However, the device for determining knocking described in Japanese Patent Laying-Open No. 2005-330954 uses a product of the value representing a deviation of the waveforms from each other and the value representing magnitude of the vibration, and hence if the magnitude is significantly great while the waveforms differ from each other, erroneous determination that knocking has occurred may be made even though knocking has not occurred. In this case, there arises a problem of excessive implementation of ignition timing retard, which is to be implemented at the time of knocking.